An assembly of devices intended to be used to monitor local body-tissue chemistry for the early detection of metabolic imbalances and/or cell damage, typically after surgery or during a metabolic disorder. The assembly typically includes a dedicated catheter that is inserted/implanted into tissue (e.g., brain, liver, muscle), a pump that circulates perfusion fluid and interstitial fluid dialysate to and from the site of monitoring, a small vial(s) used to collect samples of dialysate, and an analyser used to determine and display concentrations of analytes (e.g., glucose, lactate, pyruvate) in dialysate samples.